The present invention relates to apparatus for machining, by electro-erosive electrical discharges, an electrode workpiece by means of an electrode tool, the apparatus comprising means for relatively displacing the electrodes along the axis of relative penetration of the electrode tool into the electrode workpiece and along the motion of an electrode relative to the other effected in a plane normal to that axis of penetration.
Control of the relative feed motions of the electrodes, in an EDM machine, can be obtained by way of several well known methods.
One of such methods consists in feeding the electrode tool into the electrode workpiece while simultaneously increasing progressively the eccentricity of the translation motion such as to provide in the electrode workpiece a cavity having a shape substantially corresponding to the geometry of the electrode workpiece. Such method is accomplished, for example, by means of an apparatus as disclosed in U.S. Pat. No. Re. 26,970.
Another known method consists in varying the amount of eccentricity of the translation motion simultaneously with the penetration of the electrode tool into the workpiece, such as to provide the lateral surface of the workpiece with a shape different from that of the electrode tool. The apparatus disclosed, for example, in U.S. Pat. No. 3,539,754 permits to vary the eccentricity of the translation motion proportionally to the machining axial progression such as to provide the lateral surface of the workpiece with a predetermined taper.
Another known method consists in effecting a three-dimensional extension of the electrode tool by causing the electrode tool to describe a translation motion inscribed on a hemisphere. Such a method, which permits to increase the precision of machining, is achieved by means of a structure such as described in the published German patent application No. 2,410,335.
Until the present invention each of those methods could be accomplished only by means of separate specific machining control arrangements, and it was necessary to shift equipment each time a user wanted to shift machining method. The novel control system for the electrodes of an EDM machine, according to the present invention, permits to operate according to any one of the machining processes briefly described hereinbefore, without requiring any change of equipment. The present invention provides means for obtaining a variable signal or value obtained by means, known in themselves, consisting in integrating, relative to time, the difference between a signal or value representative of the machining conditions and a reference signal or value, and by providing means for apportioning, or dividing, the signal or value thus obtained into a first and a second electrical signal or value, means for balancing the apportionment and means for controlling the relative position of the electrodes both along the axis of penetration of the electrode tool within the electrode workpiece and the amount of eccentricity of the translation motion, respectively, as a function of the first electrical signal or value and as a function of the second electrical signal or value.
One of the many advantages of the invention is to permit to control at will the direction in which the translation motion is effected, in a manner which is simple, precise and economical, and to achieve a permanent control of the relative position of the electrodes in all directions selected between the direction of the axis of penetration of the electrode tool into the electrode workpiece and the directions perpendicular to the axis of the penetration. More particularly, the present invention is well adapted for use in cooperation with mechanical motion translation drivers having an eccentricity whose amount is controlled by a single servo motor.